HVAC Zoning: Do You Need It, or Not?
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- เผยแพร่เมื่อ 25 ส.ค. 2021
- We get asked this a lot, so here we're trying to explain as concisely as possible why zoning is often a symptom of a badly built home enclosure (or a poorly planned McMansion, obviously). If heat is bleeding through the skin of a home at a controlled rate in every room, there's no need to zone the HVAC system to give special attention to a weak link. There are no weak links in a well-tuned home enclosure, and so your HVAC system can be simpler with fewer components, and more sure to effectively condition the home.
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We are currently building a new house in east Texas and have decided on a zoned heat pump. My 88 year old dad has moved in with us and it's impossible to keep the temperature where we are all comfortable. So we have 3 zones, living/dining/study on 1, master bed/bath on 2, guest beds and bath on 3. There is an additional small outlet/inlet running off zone 2 into our fully conditioned attic.
My want for zoning comes more from a point of wanting different temperatures in these zones. I realize that in a properly built home, keeping one even and consistent temperature does NOT require zoning, but I'm not sure how else I could keep, say, different bedrooms at different temperatures. For example, MY master bedroom will end up with the thermostat set at somewhere around 63-64 at night, because I love it COLD. Anyone else in the house will inevitably complain that "its too cold, can't you turn the thermostat up?????" And the answer will be a loud NO
OOOOHHH that’s a good one. Makes me really want to try and tune a home to deliver that without zoning- I bet it’s possible!
Something like that could probably be remedied by a portable air conditioner just for your MB.
@@HomePerformance My whole goal is to try and figure out what the best ways to accomplish what I want. And I’m definitely at a loss for how to make this one happen. My real wants with whatever sort of setup are to have absolutely bo need for a stand-alone air purifier, so air filtering constantly. I want one control to set for the humidity, ventilation and temperature control for all the main areas, but each bedroom with some means of having its own temperature, as I don’t know that it’s necessary to freeze the entire main living areas of the house at night to my 63°. I also realize that in a ‘normal’ house, this kind of thing means each ‘zone’ is independently fighting the exterior temperatures, but in a high performance house, each of these areas are going to fight each other.
Dude, I am going to brainstorm a vid for you
@@HomePerformance i would love to see that.
its pretty common downunder to have bedroom temps a lot colder. (in fact many people here complain that 64f is to hot but thats another story).
we generally do not have HVAC here (have heat pump per room which gets expensive), but ducted heat pumps are becoming more common. so zoning is an issue. i have toyed with the idea of dual heating/cooling systems so bed rooms can be maintained at a different temp.
Ok Corbett, here we go:
1. Agree that zoning done wrong has given zoning a bad name. We have successfully used zoning on existing 2 story homes with 1 system, 1 thermostat and given both floors comfort by adding zoning and a second thermostat. Yes, we didn’t address the home performance problems, but we weren’t called for that and we were working within a budget.
2. Every and I mean every multi level high performance home that I have ever done has been zoned. One main reason is that the loads per floor, or per zone, are smaller than the smallest tonnage of conventional HVAC equipment and I didn’t want to oversize.
3. Zoning prevents over sizing. Especially if you run simulations where you diversify the load. For example, if we have a total block load of 4 tons, and the home is divided into 4 zones, we usually put in a 3 ton system because not all the areas in the home are at peak load at the same time. We can move that 3 tons around to follow the sun or occupant load.
4. Zoning is code compliant. In NC we are not allowed to use a single system for multiple floors unless it is zoned, high performance home or not, the code doesn’t care. The only other option is each floor gets its own unit and that gets expensive.
5. Zoning keeps the budget down. Initial cost and total cost of ownership. I would argue energy bills would be lower compared with multiple separated systems, as long as multi stage or variable speed is used in zoning.
Now with all that said, if you are going to zone, you gotta do it right. You must use multi stage equipment or variable speed/ communicating systems. Never ever use a bypass. Size ducts and divide zones evenly so that a worse case scenario doesn’t try to force too much air through too small ductwork. Set up the zone controller so that it doesn’t kick into high stage with only one zone calling. Put returns in open areas, never in small rooms to avoid pressure issues when that zone isn’t calling. When done properly, I really think a zoned system is better than 2 units. Commercial buildings have been using zoning for decades. They do it right. With variable volume blowers controlled off supple static, multiple stage cooling, controlled off supply temperature, and each zone had a Variable Air Volume box with a damper and sometimes a blower. There is no reason why a resi zoned system can’t work well too.
Thought? 🍻
THANKS for such a deep and reasoned comment, Tim! Here are the thoughts that spring back from your points, just to take the conversation deeper:
1. Existing homes of typical 'performance' are not included in my concept, as I'm sure you picked up, and I agree that band-aids are very helpful in many cases.
2. I'm very interested in why the floors must be conditioned separately in your experience... I think you may be surprised to monitor how often the zones call separately in a high performance home- in my experience, it won't happen. If the heat bleed is slow as molasses everywhere, then the home acts a lot more like one big blob than a bunch of separate spaces connected by passageways. Stack effect does not result in stratification, for example.
3. Again, I don't think the load 'moves' in a high performance home as much as you think. The big lift is getting all the solid materials to temperature- once all the 'stuff' in the house is the same temp, the air temp is just a drop in the bucket, it can vary a bit without the mean radiant temp moving at all. This is also why I don't recommend setback thermostat settings in a home like this- set it and forget it, the house is a huge ship that doesn't steer easily (which is good).
4. WOW. That is f'd up. THIS IS THE WHOLE THESIS RIGHT HERE, and I think this should have been point #1!
5. I don't disagree.
Keep up the great work as a creator buddy, and thanks for watching! Creators get a permanent pass on watching other creators if they don't have the time, imho, so I appreciate it.
@@HomePerformance the whole reason why each floor has to be conditioned separately is code compliance. So this forces our hand to have to either zone or use separate equipment. I agree 100% with your last comments, all of them. The house does act like a thermal blob and is slow to react. The only exception might be a room with wall to wall souty or west facing glass that may warm up at a quicker rate than the rest of the house.
If it were not code required, I agree a WELL DESIGNED HVAC system in a HIGH PERFORMANCE home could be controlled off 1 tstat, no zoning, with perhaps a few remote sensors that would be programmed to "follow" the load, like what the Ecobee 5 does. But NC code forces our hand because of all the crappy 2 story houses built in the 80s and 90s that have an 8 degree temperature difference between floors!
Keep up the great work! I'm reminded of a phrase in the Bible that "iron sharpens iron".
Corbin, my complements on a very direct and well spoken video. Keep up the good work educating the masses.
Thx Dave
In my experience, you still can get temperature and humidity stratification between floors of a high-performance home. This is why we typically mechanically separate floors and remote spaces. Typically we doing this with separate air handlers with VRF or variable speed units on a hydronic distribution system.
Interesting- I haven’t seen stratification significant enough to bother about if the systems are all high performance- plenty of room for error in any trade, of course. Better safe than sorry.
@Home Performance We do install zoning under certain circumstances. We won't install zoning with a single stage system--it has to be a minimum 2-stage compressor or (preferably) variable speed. Since Manual J & D are used in design, not many of our design houses are zoned unless they meet our criteria. For example, if a homeowner wants one room (like a master bedroom or a FROG) to be cooler or warmer than the rest of the area, or if they have a relatively small FROG, we will usually use a Mitsubishi ductless or ducted unit for that area. You are correct, zoning can definitely cause more problems than it fixes, if not done correctly.
Amen Shawn- the bigger question is why people think they want a room that’s tempered differently than the others…
@@HomePerformance I agree. More and more homeowners want to have their temperatures set at very cold temperatures when they sleep. I told one who wanted their bedroom to cool to the low 60's that what they need is a walk in cooler or wine cellar to sleep in.
Stick it to em straight, Shawn
My house has a mother in law suite addition. I’m adding a ground source heat pump. She likes extra heat and less a/c than the rest of the house. Would a zone system be better than installing two separate heat pumps?
I take it thought that the control for the vent hood operation and how that interacts with the rest of the house ventilation (via the exhaust damper / increased intake) is not considered zoning in this definition.
Right, in the HVAC industry ‘zoning’ is a specific thing.
Interesting to hear this. My builder and a few HVAC people have also told me they don't recommend zones, but I thought they were just trying to cut costs. :)
I am very interested in zones for two reasons.
1. It seems worth it to me to have the master on a zone so I can be cool at night and the 3500 sq ft rest of the house doesn't have to spend the energy to stay that cool. Is the ROI not there?
2. We will have a media/exercise room that will be empty for long stretches, then suddenly have many people or one sweating person. The media room will also have interior insulated walls and hopefully a somewhat tight fitting door. I'm worried a tiny miscalculation in the Manual J will mean it's too hot or cold. And also.... same question about ROI. If it's regularly unoccupied for 72 hours we could keep the door closed and the temp at 80.
So many new ideas for future videos in these comments, holy cow! I’m on the case.
I can't find which publication mentioned it for the NIST's NZERTF house in Maryland, but the researchers found something like a 6-degree difference between the first and second floor. The conclusion of the paper suggested testing if a ceiling fan over the stairs could help mix and reduce that stratification.
Ceiling fans are an integral part of any high performance home's HVAC system, high five on that one
What if you have a home where certain rooms you only use when you have guest periodically? You could have a a ductless minisplit, which would be ideal, but if you already have a central hvac system, then maybe zoning is a good way to deal with what you already have cost effectively. If you are planning a completely new hvac system for a new construction home, then zoning doesn't seem like a good idea.
TLDR IMO zoning is a good way to deal with an existing hvac system where you don't use certain rooms for much of the year.
I love your piano skills! :)
💋
I am sealing my house (spray foam and windows). I will be surprised if it ends up super sealed. however due to space I am looking at ductless ducted systems. creating a different kind of zoning. Bed rooms on one unit and day rooms on another. what are your thoughts? keep the cooler temp in the spots where the people are. let the others just maintain or get the bleed off.
In a high performance home (which the spray foam contractors SHOULD BE GUARANTEEING), a setback thermostat becomes irrelevant. The materials can and should be maintaining the same temp continuously- letting the air temp slide around from day to night ends up just being uncomfortable, and I’d challenge even the DOE to provide proof that it saves money in a home like that- every morning you’d have to drag the materials back to the right temp, which takes more work. Watch this:
th-cam.com/video/IDmkgAqr_8s/w-d-xo.html
Zoning, meh
Multiple systems, much better.
Small footprint with high height, or otherwise 4 floors. Stack effect really comes into play here. Air sealing helps, but I find it doesn't solve the issue of temp fluctuations from floor to floor.
Especially in zone 5 or 6 where you have good winters and summers.
My Future building goals are one system per floor for independent control.
I agree that zoning is NOT necessary for most new construction homes that are high performance. Get your HVAC contractor involved in the planning phase of a build. If you want a comfortable home the HVAC system WILL require space and a good design. Also, a high performance system will be a larger investment up front. All metal ductwork that is custom made, sealed, and insulated, is going to take way more time to design and install.
For large multi story homes a zoned system or going with 2 or 3 separate systems may be a good solution.
100%- we should NOT be heaping all of a homes problems in the lap of the HVAC team. And I think if we can make it plain that the more expensive, custom metal job you’re selling will work for 100 years (changing out the equip obviously), then a lot of people would find the means to pay for it.
Thanks for the video. Do you know of a good online place to get a manual j?
I don’t think that exists, but there are plenty of individuals who are great at them. I can do it if you’re not in a hurry.
Is it smart to do zoning system for a townhome that’s only a little over 1100 sq ft? Currently have two systems. Is it smarter to simply get the two replaced or to look further into the one zoning system?
If your airsealing and insulation is well done, you probably have no need for zoning. Also, two systems for 1100 sq ft is a guarantee of oversizing.
Tested a house last week with a zoning system. The ductwork (return in particular) had holes I could stick my arm in up to my elbow. No way this system would work effectively. 2nd floor return vents couldn't even turn the anemometer.
Yikes
What about when you have 2 story house and a VRV system that is always on? (upstairs is warmer then lower floor wherer a single thermostat is located). Just manual dampers only option to balance air in summer, then open them all up in winter) warm air rises right ?
In a high performance home (airtight and well insulated) stack effect doesn’t result in a warmer upper floor.
@@HomePerformance stack effect is warm air rises escapes through ceiling via leaks. Air comes into replace it and is never ending. But if ceiling is sealed hot air still rises. It’s easier to cool but will never match lower floors if ac cuts off when Lower floors are at set temp. You will always have some leaks. Doors open at some point in the house. So hot air rises. You need to ensure upper floor either has main thermostat or more cold air flows upstairs to off set hot air rising.
I’m telling you, if you have circulation and intentional pressure imbalances, it won’t happen. Again, I understand you can’t possibly believe it until you feel it, but I feel compelled to try.
What about a barndominium? We have a 32' wide great room with 20' ceilings, separating the master suite from the guest bedrooms. We will have radiant heat in the floor and closed cell foam top to bottom. We are building in Virginia.
You need a Manual J heat load calculation.
How do I solve the issue caused by a two story house with a two story living room?
Ceiling fan Roger my man!
Corbin-?important to note dampers zoning are 1) additional design burden )2 additional expense 3) additional thing to go wrong(can u access the damper?) that said I think your perspective also assumes open floor plans and always on ceiling fans - you have fans in EVERY. Room right? So I think a competent designer/installer can easily justify a two zone system in two story situation we here spaces equal volume and different facedas glazing e.g enclosed basement first floor with (35per cent glazing
In a modern home you want zoning combined with a control system ex. Knx, to tune temperatures based on occupancy.
I need different temperature depending on room. The explanation here talks about distribution, is not really accounting for conditions.
Get it balanced. Then new season, wind and weather patterns change. Now tuning has to be done again, several times a year.
Fun times
In my area and experience; no one here can even fathom a high performance setup. Manual j in 1 min before they leave the house and toss in a unit that in the past has worked for others.
Very frustrating.
What a great sales motto: ‘Manual J in 1 Minute or Your Money Back’
Great discussion. IMHO to convince people, you need to have a good discussion about comfort, and if that is successful then transition to how to make it happen with a high-performance home with HVAC/ERV. Most homes in the US are not high-performance so to achieve what people sense as comfort they are applying bandaids because of improper insulation, lack of an air barrier, incorrect window sizing coupled with improper windows, poor humidity control, and erratic ventilation among other issues. Robert Bean Retired ASHRAE & Distinguished Lecturer (Linkedin) may be helpful in planning the comfort discussion.
in theory yes, but what size home are e talking about ? a 2,000 sq foot house is NOT all that large -nd what is your largest room ? a large open floor plan home will never feel right with mini splits. Tho i concede having a ver robusta separate ventilation system/trunk like your house has mitigates greatly
I stand by it, even for a 5000 sq ft home that’s well laid out. And our big rooms are 36x24 with 13 ft average ceilings, fyi.
Why aren't ducts pvc ? Why metal ?
Cost, and they just don’t make PVC big enough around.
3000 sq ft home, 9 foot ceiling equals 27000 cu ft volume. What capacity heating/ cooling system do I need ?
Jimmy, you should definitely check out my Manual J vid. No way to tell size requirements from just that info.
how my house SHOULD have been built, gee thanks